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A stress fracture is a fatigue fracture resulting from repetitive, excessive load applied to a normal bone.1–4 On the other hand a "normal" amount of load applied to a weak or structurally abnormal bone results in an insufficiency fracture.

The reported incidence and the site of stress fracture vary by sport (Table 31-1).1–3 Stress fractures are more frequent in track and field athletes than in other sports. The incidence can range from 3% in soccer players to 15% in runners, and stress fractures account for between 7% and 20% of all injuries seen in sport medicine clinic.5 Overall, stress fracture of the tibia is the most common. Stress fractures are more common in females, some studies reporting a rate 10 times higher than males.

Stress fractures are caused by overuse. Bone is constantly remodeling, and under the repetitive stress of athletics resorption of the bone in a particular area (e.g., the lateral femoral neck or the tibial shaft in runners) may outpace bone formation (Figure 31-1). This follows an increase in training intensity, often within 6 to 8 weeks of the change. High-performance athletes often have a protein calorie imbalance and train so intensely that it is difficult for them to take in adequate protein, calcium, and other nutrients without eating a high-calorie, high-protein diet.6,7 It is theorized that multiple factors contribute to eventual fatigue fracture of the bone, and in addition to the excessive physical activity, other factors include bone density at the site, the geometry of the bone, the direction of the load, the vascular supply at the site, the muscle attachments, and the specific sport.1–4,8

Female athletes participating in sports that require maintaining a thin body habitus may engage in weight control by restricting caloric intake at the same time expending significant calories. This is often complicated by menstrual irregularities, amenorrhea, and a hypoestrogenic state. In addition to caloric deficit, these athletes also have dietary intake deficient in calcium, vitamins, and other essential nutrients. A higher incidence of stress fractures is reported in these female athletes.